July 10 (Bloomberg) -- The investigation into why pilots
flying Lockheed Martin Corp.’s F-22 Raptor keep getting dizzy
and disoriented is focusing again on whether the plane’s oxygen
system works well enough at high altitudes, lawmakers said.

Honeywell has said that the system works well, and during a
yearlong investigation the Air Force has turned in recent months
to other possible causes for the symptoms of hypoxia, or oxygen
deprivation, including ill-fitting pressure vests worn by the
pilots and the possibility of contaminants in the air.

Citing information they obtained from the Air Force, the
lawmakers said an Air Standardization Coordinating Committee
“apparently has concluded that the quantity of oxygen required
for pilots to perform full F-22 operations may, in fact, be
greater than what is supplied” by the oxygen system.

The assertions were made in a letter today to Air Force
Secretary Michael Donley in which the lawmakers sought
additional answers to the mystery of the F-22’s oxygen-related
problems.

Honeywell’s Comment

A Honeywell Aerospace spokesman, Nathan Drevna, said in a
statement that the company’s oxygen system “is performing as
designed in accordance with U.S. Air Force specifications.”

“Honeywell continues to support the USAF and the F-22
industry team in understanding the cause for the physiological
incidents leading to various F-22 fleet issues,” he said.

Unable to explain episodes of dizziness and other ailments,
the Air Force has been looking at a variety of possible causes,
from the prosaic -- hoses, masks and the pressure vests -- to
the top-secret coatings and adhesives used in the plane’s radar-absorbing stealth skin that makes it harder to track.

The lawmakers suggested on a conference call with reporters
today that the Air Force is returning to a lack of sufficient
oxygen as the leading theory for the hypoxia problem.

“It seems like we’ve come a bit full-circle back to
that,” Warner said.

Kinzinger, urging caution, said, “This may be the leading
theory right now, but in the last few times we’ve had a leading
theory, we’ve been burned.”

Pressure Vest

The Air Force focused last month on a pressure vest worn by
F-22 pilots that “increases the difficulty of pilot breathing
under certain circumstances,” according to a statement from Air
Combat Command.

Even after the Air Force instructed pilots to stop wearing
the vests, additional hypoxia incidents were reported, most
recently on July 6.

At least two dozen pilots and six ground-maintenance
workers have reported symptoms associated with a lack of oxygen.
There have been at least 11 reported incidents since the plane
resumed flying operations last year after a four-month halt
because of safety concerns.

Warner and Kinzinger said in the letter that there have
been additional hypoxia-related incidents that the Air Force
hasn’t disclosed, including a July 6 incident at Joint Base
Pearl Harbor in Hawaii, a “restricted airflow” incident in
late June at Joint Base Langley-Eustis in Virginia, and a May 31
incident at Tyndall Air Force Base in Florida in which a pilot
hit the runway without extending the plane’s landing gear.

Earlier Finding

Gregory Martin, a retired general who headed a study of the
F-22 for the Air Force Scientific Advisory Board, told reporters
at a March 29 Pentagon briefing that the plane’s oxygen system
“might not produce as much oxygen as it would when it was not
under G,” or a high level of acceleration. Still, he said, the
oxygen level was “never in an area of concern.”

The assertions by Warner and Kinzinger indicate that the
Air Force may be revisiting that assumption.

In May, Defense Secretary Leon Panetta imposed new safety
measures that include limiting flight durations and speeding the
installation of a back-up oxygen system.

Lockheed Martin, the world’s largest defense contractor,
won a $19 million contract in June for the back-up oxygen supply
system, which is scheduled to be installed by the end of next
year.

Warner and Kinzinger asked the Air Force in their letter to
specify whether Lockheed’s new contract was awarded without
competition.